Emily Dickinson Lexicon

CATH'E-TUS, n. [Gr. καθετος. See Catheter.]

In geometry, a line or radius, falling perpendicularly on another line or surface; as, the two sides of a right-angled triangle. – Encyc. Cathetus of incidence, in catoptrics, is a right line drawn from a point of the object, perpendicular to the reflecting line. Cathetus of reflection, or of the eye, right line drawn from the eye, perpendicular to the reflecting plane. Cathetus obliquation, a right line drawn perpendicular to the speculum, in the point of incidence or reflection. In architecture, cathetus is a perpendicular line, supposed to pass through the middle of a cylindrical body. Also, the center of the Ionic volute. – Encyc.